Process of chromium plating vented piston rings



Aug. 28, 1962 D. A. PAULL ETAL 3,051,633

PROCESS OF CHROMIUM PLATING VENTED PISTON RINGS Filed March 16, 1959 2 Sheets-Sheet 1 INVENTORS DONALD 4. PAULL &

BY DONALD J. WILSON ATTORNEYS Aug. 28, 1962 D. A. PAULL ETAL PROCESS OF CHROMIUM PLATING VENTED PISTON RINGS Filed March 16, 1959 2 Sheets-Sheet 2 INVENTORS DONALD A. PAULL & DONALD J. WILSON BY Mb ATTORNEYS United States Patent Ofiice 3,051,633 Patented Aug. 28, 1962 3,051,633 PROCESS OF CHROMIUM PLATING VENTED PISTON RINGS Donald A. Paull and Donald J. Wilson, Muskegon, Mich.,

assignors to Sealed Power Corporation, Muskegon,

Mich., a corporation of Michigan Filed Mar. 16, 1959, Ser. No. 799,676 16 Claims. (Cl. 20424) The present invention relates to chromium plating of vented piston rings, that is, piston rings grooved exteriorly at outer faces around the rings, from the bottoms of which grooves spaced oil passing slots are cut radially through to the inner curved faces of the rings. Such a piston ring, above and below the outer circumferential groove around it, has narrow cylinder wall contact lands, the outer curved faces of which, for longer wear, are preferably chromium plated. Such plating must be of substantially uniform thickness over said faces of the lands.

Chromium plating such rings, to obtain the desired uniformity of thickness, cannot be accomplished by the usual methods of plating directly on the ring periphery because of excessive gassing which takes place in the vent slots of the piston rings. Gassing results in chromium plating of varying thickness at the slotted portions of a piston ring and the bridge portions between such slotted portions.

We have invented a practical and successful method of chromium plating such slots vented piston rings whereby the cylinder bearing lands of the rings are uniformly plated over their entire peripheral faces. An understanding of our invention may be had from the following description, taken in connection with the accompanying drawing in which,

FIG. 1 is a plan view, partly broken away and in section, of a slot vented piston ring to which our invention is applied.

FIG. 2 is an elevation showing a number of such piston rings mounted on an arbor of the present invention preparatory to plating. 1

FIG. 3 is a fragmentary enlarged transverse section taken along'the line 3-3 in FIG. 1 through a grooved piston ring at a bridge portion thereofr "FIG. 4 is a fragmentary enlarged transverse section taken along the line 44 in FIG. 1 through the grooved piston ring at a slotted vent portion thereof. 1

FIG. 5 is a section similar to FIG. 4'after the first plating coat at the exterior of the piston ring, extending through such slots and to the inner side of the ring, has been deposited.

FIG. 6 is a section similar to FIG. 5 after the final coating of chromium plating has been deposited.

FIG. 7 is a perspective view of the clamping sleeve.

FIG. 8 is a sectional view along the line 8-8 in FIG. 2.

F16 9 is a sectional FIG. 8.

' FIG. 10 is a perspectiveview showing a slotted tube as distinguished from the solid tube of the arborillustrated in FIG. 2.

The piston ring 1 of conventional circular form, parted at one side, before the vent slots are cut has a continuous groove 2 around it at its outer curved side, midway between its upper and lower flat sides. There is left narrow bearing lands 3 at opposite sides of groove 2, as in FIG. 3. Y

The vent slots 4 are cut'from the bottom of the groove radially inwardly through to the inner periphery of the ring. Such slots extenda'round the ring in spaced relation in succession to each other. The slots 4 are view along the line 9-9 in sawed. or otherwise provided in the body"'of the" ring, 4

as shown in FIG. 4, slotting from the bottom of groove 2 radially to the inner side of the ring. Slots 4 are separated circumferentially by bridge portions 5.

In accordance with the present invention, the rings 1 are mounted on a fixture or arbor 6 for plating. Arbor 6 comprises a bar 7, the upper end of which (not illustrated) may be hook shaped to enable suspending the bar from a cathode rail. In the plating operation hereinafter described, the arbor 6 with a plurality of piston rings mounted thereon serves as the cathode. On the bar 7 of the arbor 6, there are arranged two end collars 8 and 9. Collar 8 is fixed on car 7 while collar 9 is axially shiftable on the lower end of bar 7 but is prevented from rotating relative to the bar by means of opposed keys 10 projecting from the bar and engaging within opposed keyways 11 on the collar. The inner opposed faces of collars 8 and 9 are counterbored as at 12 to provide an annular shoulder 13 on each collar within which a tube 14 is arranged to be engaged. Tube 14 has an outer diameter slightly smaller than the inner diameter of the piston rings 1 in their free expanded condition illustrated in FIG. 1. The outer diameter of tube 14 is accurately machined to correspond with the inner diameter of ring 1 in its normal operating condition; that is, contracted from the expanded condition illustrated in FIG. 1.

To assemble the rings 1 on the arbor 6, a predetermined number of piston rings 1 are slipped over tube 14 and the tube 14 with the rings thereon is then engaged within the annular shoulder 18 of the upper collar 8. Thereafter, the lower collar 9 is slipped over the end of shaft 7 and engaged with the lower end of tube 14. A square bushing 15 is arranged on the lower end of bar 7 adjacent the lower collar 9. Bushing 15 is likewise provided with opposed keyways 16 which engage opposed keys 17 on bar 7 to prevent relative rotation between bushing 15 and bar 7. A nut 18 is then threaded over the lower end of bar 7 and tightened only sufficiently to hold the members in loosely assembled relation. The individual rings 1 which are loosely supported on the arbor are shifted circumferentially to stagger the gaps 20 between the opposite ends of each ring. Gaps 20 are so staggered that each gap is axially aligned with a bridge portion 5 on each of the next adjacent rings on the arbor. With the gaps of the ringsaligned in this manner, the rings-are then in a condition to be tightened on the tube 14 so that the inner periphery of each ring. snugly embraces the outer periphery of tube 14.

One relatively simple way of closing the rings around the tube 14 involves the use of a tubular clamping sleeve 25 which is split axially into two half sections hinged to.- gether as at 26 so that it can be wrapped around the rings'on the arbor and tightened by means of nuts 27 so as to bring each ring into snug contact around its inner periphery with the tube '14. Thereafter, the nut 18 is tightened with considerable pressure suflicient to hold the rings in the closed position when the hinged sleeve is removed from the arbor. I

The length of tube 14 is determined in relation to the number of rings assembled on the arbor so that when nut 18 is tightened, .axial pressure is exerted by collar 9 on collar 8 through the stack of rings rather than through the tube 14. Thus, as shown in FIG. 1, the length of the stack of rings 1 on the arbor 6 is less than the length of the tube 14 and there will be a small clearance between the end or ends of the tube 14 and the bottom of one or both counterbores 12 in collars 8 and 9. With the gaps 20 staggered as described previously, the bridge sections 5 of all the rings will be aligned axially so that upon tightening of thenut 18, there will be no tendency for any of the rings to collapse or distort. "As pointed out above, the outer diameter of tube' 14 is accurately maa,051,es3

3 chimed to'correspond"to' -the inner diameter of rings 1 whenclosed sothat the tube 14 effectively closes the inner ends of vent slots 4.

With our invention, the ring with vent slots 4 is first plated with 'a -metallic coating which, preferably, is of bronze. ThebI'OIlZfi composition for best results is'an alloy of 12% tin'and 88%"eopper. However, such percentagesmaybeappreciably varied,'-reducing the tin content, as satisfactory "results are obtained with an initial copper*plating---alone, 'or through alloys of copper and tin fromione' percent or less to the maximum 12% described. The copperlor bronze plating is very quickly deposited in-a conventional plating bath which-has superior demonstratedthrowing power. 'There will be a thin copperor bronze coating over the ring at the outer peripheral faces of lands 3-,'-the groove 2 andthe sides of the slots'4. Such copper orbronzeplated coat is indicated at '21, shown highly exaggerated in thickness in FIGS. 5 and 6. His quickly deposited on the cast'iron'outer peripheral surfaces of the piston ring lands 3,'groove 2 and slots 4 with'a minimum of-gassing occurring 'in' the slots 4 and other recessed portions.

Following the copper or bronze initial plating, the rings are then chromium plated in a chromium plating bath of well known composition and following conventional chromium pl-ating'practices. The chromium plating, indicated at 22in FIG. 6; deposits over the copper or bronze plating at '21, being thickest at the peripheral surfaces of lands3'and diminishing in thickness inwardly therefrom. It likewise is exaggerated in thickness as shown in FIG. 6.

his the initial copper orbronze plating of the sides of the slots 4'and the use of tube 14 which prevent objectionable-gassing upon-subjecting the rings to the subsequent chromium plating.

The method followed is to first place or clamp the rings 1 on the arbor 6 as described, and then subject them to the usual and conventionalalkalineelectro-clean, rinse and pickle operations prior to any plating. The arbored rings 'are then placed in a high throwing power bronze or copper bath sufficiently long to get complete copper or bronze coverage in all recessed areas in the outer groove and vent slots. The arbor with rings thereon is then-removed from such copper or bronze plating bath, rinsed and then placed in the chromium platin'g'bath and. plated the same as they'would be'if the rings were not slotted.

:We have found that when plating chromium on copper ortopper alloysjthe electro-potential'is much greater than-'when'plati'ng directly on iron, so thatthe'throwing power with'chromium is greatlyenhanced. Further, havingja complete covering of copper orbronze in the-low current density areas, such as the vent slots 4, the chromium plating solutioniis Prevented from reacting with the'iron of the'rings to produce excessive gas, which, if produced in large quantity, gets to' the'bath surface by way of the'ventslotswith attendant disadvantages and results of non-uniformity of chromium plate deposit. By arranginglthe rin'gs'on the arbor so that the inner ends of the'vent slots "4are sealed'by tube 14, the current densityflin the .area' offthe slots more nearlyapproaches thecurrentfdensityjatthe'bridge portions 5. This contributes'substantially' to the production of a chromium plating of generally uniform thickness on the outer peripheral surface of the .lands' 3' both at'the slots. 4 and the bridge portions '5.

'One ofthe important factors contributing to generally'funifo'rm thickness of the chromium "plating on the outerperipheral surface ofl'the lands 3.both at theslots 4 the bridge'portions 5 is that the vent slots are closed during thechro'mium plating operation by a removable and'reusable member such as exemplified by the tube 14. Tube '14 preferably is. an electrical conductor made from any" suitable metalor alloy such as steel and causes the current'd'ensity 'in the area of the slots 4 to-approxima-te the current densit'yin the area of the bridge portions 5. If desired, "tube ..14 can be made .of an electrically nonconducting synthetic or plastic material which is inert to 'theelectrolytes in which it will beimmersedin the her, or a thermosetting material such as phenol formaldehyde and phenol-fur'fural molding compounds.

Preferably, tube 14 ,is.not slotted; but if desired, the tube can be slotted. Such a slotted tubeis shown in FIG. 10 and designated 30. If the tube is a welded steel tube, then the slot 31-is preferably cut'the full length of the tube at the weld. When the tube is a'slotted tube, it is inserted into the rings 1 so that the tube slot 31 lines up with the ring bridgesS. The tube will be compressed with the rings when the ring gaps 20 are closed so that the slot in the tube will also be closed or substantially closed and this technique assures good contact of the tube with the inner diameter of the rings.

The important features of the present invention reside primarily in the closing of the inner ends of the vent slots 4 and the initial copper or bronze plating of the sides of the slots, both of which features cooperate to reduce to a minimum objectionable gassing during the subsequent chromium plating operation. The plating procedures employed are not critical and are in accordance with conventional practice. In general, any of the following plating sequences will produce satisfactory results:

(1) Cyanide copper plate followed by chromium plate.

(2.) Cyanide copper strike followed byacid copper plate and then chromium plate.

( 3 Bronze platefollowed by chromium plate.

Cyanide copper plating is satisfactory but generally producesa coating which is less dense and more porous than the other two pro-plating baths mentioned above. A coating denser than that obtainable with a cyanide copper plate results from an initial strike in the cyanide bath with a completion-of a flash coating in the acid copper bath. Best results are obtainable by pre-plating in a bronze bath. This has the primary advantage of the deposition of a'dense, smooth plate'in one operation. Furthermore, a bronze plate has a consistently high throwing power and thus insures minimizing of gassing problems in the chromium bath.

The folowing data is illustrative of'the various plating baths that maybe employed:

The voltage employed-will va'ry with the sizeof the work piece and the distance between the work piece and the anode. As anzexample, however, at 4 volts'and in a period of 4 minutes, a copper plate has been, produced on rings with a thickness of .0002.0004".

(2) .Aczd Copper Item Range Preferred 22132 23 4 (c Sodium Chloride oz./gal 030-.040 .033 (11.) Bnghteners to 'Suit- 1 (0 Cathode Current Density. a lit 20-80 25 (1.) Temperature. -95 (g.) Anodes ..d. Copper A thin even coating of approximately .0002" in thickness may be obtained at 2-4 volts within to minutes.

(3) Bronze Preferred In a period of about seven minutes at 3 volts, a plate of about .0003-.0005" in thickness can be deposited.

(4) Chromium Plating At between 7 to 9 volts, a plate of about .004.006 can be deposited in a period of about 3 /2 hours.

With respect to the plating procedures, the thickness of the coating is not critical. The values given above may therefore vary within relatively wide limits. It is important, however, that the thickness of the coating around the peripheral faces of the lands 3 of the ring he generally uniform both at the vent slots 4 and the bridge portions 5. The uniformity in coating thickness is attributable primarily to the overall plating procedure involving closing the inner ends of the vent slots 4 and pre-plating with copper or bronze.

Thus, it will be seen that we have provided a novel and successful method of effectively chrome plating a piston ring provided with radially extending oil venting slots. The method disclosed herein is highly desirable in that it enables the piston ring to be completely machined and finished prior to plating.

This application is a continuation-in-part of our pending application Serial No. 770,698, filed October 30, 1958, now abandoned, the latter application being a continuationin-part of our prior application Serial No. 640,009, filed February 13, 1957, now abandoned.

We claim:

1. The method of chromium plating the outer peripheral surface of a piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises temporarily closing said slots only at the inner periphery of the ring by applying a liner to the inner peripheral surface of the ring and while said slots are thus closed, depositing by electroplating a metallic coating or copper on the outer peripheral surface of the ring and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surface of the ring.

2. The method of chromium plating the outer peripheral surface of a piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises temporarily closing said slots only at the inner periphery of the ring by applying a liner to the inner peripheral surface of the ring and while said slots are thus closed, depositing by electroplating a metallic coating of a copper and tin alloy on the outer peripheral surface of the ring and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surface of the ring.

3. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of the rings over a generally imperforate cylindrical sleeve having an outer diameter smaller than the inner diameter of the parted rings, circumferentially closing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve depositing by electroplating a metallic coating of copper on the outer peripheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

' 4. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of the rings over a generally imperforate cylindrical sleeve formed of an electrically conducting material, circumferentially closing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve, depositing by electroplating a metallic coating of copper on the outer peripheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

5. The method called for in claim 4 wherein said sleeve is formed of steel.

6. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of the rings over a generally imperforate cylindrical sleeve formed of an electrically non-conducting material, circumferentially closing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve, depositing by electroplating a metallic coating of copper on the outer peripheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

7. The method called for in claim 6 wherein said sleeve is formed of a plastic material.

8. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of the rings over a generally imperforate sleeve having an outer diameter smaller than the inner diameter of the parted rings, closing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve, depositing by electroplating a metallic coating of a copper and tin alloy on the outer peripheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

9. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots extending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of the rings over a generally imperforate cylindrical sleeve formed of an electrically conducting metal, circumferentially closing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve, depositing by electroplating a metallic coating of a copper and tin alloy on the outerperipheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

.10. The method called forin claim 9 wherein said sleeve is formed of steel.

11.. The method of chromium plating the outer peripheral surface of a parted piston ring having radial slots eX- tending from said outer peripheral surface to the inner periphery thereof which comprises arranging a plurality of thei-ings over agener'ally imperforate cylindrical sleeve formed of an electrically non-conducting material, circumferentiallyclosing the rings on said sleeve so that the inner peripheral surfaces of the rings tightly embrace the outer peripheral surface of the sleeve and the sleeve thus closes the radial slots at the inner periphery of the rings and while the rings are thus arranged on said sleeve, depositing by electroplating a metallic coating of a copper and tin alloy on the outer peripheral surfaces of the rings and on the side surfaces of the slots therein and thereafter chromium plating the outer peripheral surfaces of the rings.

12. The method called for'in claim 11 wherein said sleeve is formed of aplas tic material.

'13. The method called for in claim 8 in which the tin comprises not more than 12% of the alloy.

' 14. The method called for in claim 8 wherein the alloy comprises substantially 88% copper and 12% tin.

15. 'The method for minimizing gassing in chromium plating the outer peripheral surface of cast iron piston rings having a plurality of circumferentially spaced slots extending from said outer peripheralsurface to the inner periphery of the ring which comprises initially closing said slots only at the inner periphery of the ring by applying a liner to the inner peripheral surface of the ring and while said slots are closed electroplating a metallic coating of copper on the outer peripheral surface of the ring and on the side surfaces of the slots therein and thereafter chromium plating the outer; peripheral surface of the ring. 7 16. 'The methodfor minimizing gassingin chromium plating the outer peripheral surface of cast iron piston rings having a plurality o'f circumferentially spaced slots extending from said outer peripheral surface to the inner periphery'ofthe. ring which comprisesinitially closing said slots only at the inner periphery of the ring byapplying-a liner to the inner peripheral surfaceof the ring. and while said slots are closed electroplating a metallic coating of'a copper and tin alloy on the outer peripheral surface .of the ring and on the=sidesurfaces of the slots therein and thereafter chromium plating the outer peripheral surface of the ring.

I References Cited in the file of this patent UNITED "STATES PATENTS 1,615,585 Humphries Ian. 25, 1927 1,644,883 Johnson Oct. 11, 1927 1,970,548 Batten Aug. 21, 1934 2,367,159 Van der Horst Jan. 9, 1945 2,388,871 Scarfi Nov. .13, 1945 2,436,227 Phillips .Feb. 17, 1948 2,696,038 Hunt Dec. 7, 1954 2,812,297 Stareck et a1 Nov. 5, 1957 FOREIGN iPATENTS 409,001 GreatBritain --'Apr. 18, 1934 721,771 "Great Britain "Jan. 12, 1955 OTHER REFERENCES *Modern Electroplating,byVA. G. Grayflohn Wiley: and Sons Inc., N.Y. (1953),pages158 and 159.

Haring etaL: Electrodepositionof Chromium From Chromic Acid Baths, Bureau of Standards .BulletinNo. 346 (1927), pages 436land 437.

UNITED STATES: PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,051,633 August 28 1962 7 Donald A.;Paull et al0 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 57, for "or" read of Signed and sealed this 1st day of January 19638 (SEAL) At zestz ERNEST w SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. THE METHOD OF CHROMIUM PLATING THE OUTER PERIPHERAL SURFACE OF A PISTON RING HAVING RADICAL SLOTS EXTENDING FROM SAID OUTER PERIPHERAL SURFACE TO THE INNER PERIPHERY THEREOF WHICH COMPRISES TEMPORARILY CLOSING SAID SLOTS ONLY AT THE INNER PERIPHERY OF THE RING BY APPLYING A LINER TO THE INNER PERIPHERAL SURFACE OF THE RING AND WHILE SAID SLOTS ARE THUS CLOSED, DEPOSITING BY ELECTROPLATING A METALLIC COATING OR COPPER ON THE OUTER PERIPHERAL SURFACE OF THE RING AND ON THE SIDE SURFACES OF THE SLOTS THEREIN AND THEREAFTER CHROMIUM PLATING THE OUTER PERIPHERAL SURFACE OF THE RING. 